1. Field of the Invention
The present invention relates to a continuous junction spin valve read head stabilized without hard bias layers and, more particularly, to first and second antiferromagnetic (AFM) layers exchange coupled to the spin valve sensor for stabilizing a free layer and a third AFM layer for pinning the magnetic moment of a pinned layer of the spin valve sensor.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field in the pole pieces which causes flux across the gap at the ABS for the purpose of writing the aforementioned magnetic impression in tracks on moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read heads a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to magnetic field signals from the rotating disk. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layers are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos xcex8, where xcex8 is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic field signals from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
A spin valve sensor is characterized by a magnetoresistive (MR) coefficient that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. For this reason a spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor. When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When the spin valve sensor employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. A spin valve is also know as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer). A pinning layer in a bottom spin valve is typically made of nickel oxide (NiO). The spin valve sensor is located between first and second nonmagnetic electrically insulative read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
It is important that the free layer of the spin valve sensor be magnetically stable. During a typical construction of a spin valve sensor a bilayer photoresist is formed on top of multiple full film material layers of the spin valve sensor. These fill film layers are then ion milled to form the spin valve sensor with first and second side edges that are typically tapered at an angle xcex8 with respect to a normal to the planes of the layers. First and second hard bias layers and first and second lead layers are then deposited with the bilayer photoresist still in place forming what is known in the art as contiguous junctions of the hard bias and lead layers with the first and second side edges of the spin valve sensor. Magnetostatic fields from the first and second hard bias layers are employed for the purpose of aligning the magnetic moments of the free layer so that they are all in the same direction in a single domain state. Without the hard bias layers the free layer is in a multi-domain state with the magnetic domains being defined by numerous walls. The narrower the track width the greater the magnetic instability of the free layer. When the free layer is subjected to magnetic field signals from the rotating disk the domain walls move around which creates magnetic noise that is superimposed upon the read signal.
The aforementioned process of making contiguous junctions inherently results in a taper of the first and second side edges of the layers of the sensor. Unfortunately, the greater the angle or taper of the first and second side edges of the spin valve sensor the less the effectiveness of the first and second hard bias layers. When the first and second side edges of the spin valve sensor are tapered the first and second hard bias layers take on the soft magnetic properties of the free layer causing the first and second hard bias layers to be magnetically more soft and less capable of applying a magnetostatic coupling for stabilizing the free layer. The first and second hard bias layers are at their maximum effectiveness when the first and second side edges of the spin valve sensor are vertical or parallel to a normal to the planes of the layers. This vertical configuration has not been obtainable with the bilayer photoresist and ion milling steps for forming the first and second side edges of the spin valve sensor. Accordingly, there is a strong-felt need for a biasing scheme to longitudinally bias the free layer into a single domain state which is not degraded by sloping side edges of the sensor.
Pursuant to the above objective, I investigated a scheme employing first and second antiferromagnetic layers in contact with the first and second side portions of the spin valve sensor for magnetically stabilizing the free layer. A third antiferromagnetic layer was exchange coupled to the pinned layer of the spin valve sensor for pinning the magnetic moment of the pinned layer perpendicular to the ABS. A wafer, upon which multiple read heads were constructed, was subjected to heat in the presence of a magnetic field that was directed longitudinal to the free layer, namely parallel to the ABS along the track width of the read head for setting the magnetic spins of the first and second antiferromagnetic layers in the direction of the applied field. The heat raised the temperature of the entire wafer at or above the blocking temperature of the first and second antiferromagnetic layers. The blocking temperature is the temperature at which the magnetic spins of the first and second antiferromagnetic layers are free to rotate in response to a field applied to the pinned layer. The first and second antiferromagnetic layers were made of a material, such as nickel manganese (NiMn) or platinum manganese (PtMn) with a high blocking temperature of about 300xc2x0 C. The third antiferromagnetic layer for pinning the pinned layer of the spin valve sensor was made of a material, such as nickel oxide (NiO) or iridium manganese (IrMn) with a lower blocking temperature of about 250xc2x0 C.
The wafer was then subjected to heat in the presence of a field which is directed perpendicular to the ABS for setting the magnetic spins of the third antiferromagnetic layer perpendicular to the ABS. Even though the second temperature of 250xc2x0 C. is less than the first temperature of 300xc2x0 C., the setting of the magnetic spins of the third antiferromagnetic layer degraded the initial setting of the magnetic spins of the first and second antiferromagnetic layers. This is due to the fact that even though the second blocking temperature is lower than the first blocking temperature the magnetic spins of the first and second antiferromagnetic layers are partially rotated during the second step of setting the magnetic spins of the third antiferromagnetic layer. This degradation then reduces the effectiveness of the longitudinal biasing of the free layer by the first and second AFM layers. Accordingly, while the scheme of employing antiferromagnetic layers instead of hard biasing layers overcomes the coupling problem, the process steps in setting the third antiferromagnetic layer for pinning the pinned layer degrades the performance of the first and second antiferromagnetic layers which longitudinally bias the free layer.
I next investigated employing first and second antiferromagnetic layers for longitudinally biasing and magnetically stabilizing the free layer and a third antiferromagnetic layer for pinning a pinned layer on a continuous junction type of spin valve sensor. The continuous junction type spin valve sensor differs from the contiguous junction spin valve sensor in that the pinned, spacer and free layers of the spin valve sensor extend not only within the sensor region of the spin valve sensor but also extend into first and second side regions on each side of the sensor regions. Accordingly, each layer of the spin valve sensor extends throughout a sensor region and first and second side regions with the first and second antiferromagnetic layers exchange coupled to first and second side portions of the free layer for stabilizing the free layer and the third antiferromagnetic layer is exchange coupled to the pinned layer and extends within the sensor region and preferably extends also within the first and second side regions. The sensor region of the read head is defined by the width of the bottom portion of the spin valve sensor and the first and second side regions are located on each side of the sensor region. An advantage of the continuous junction read head over the contiguous junction read head is that first and second side edges do not have to be formed by photoresist patterning and ion milling. This saves numerous process steps and avoids a redeposition problem of material layers ion milled during the ion milling step. Further, with the continuous junction spin valve sensor the first and second antiferromagnetic pinning layers make surface to surface contact with the first and second side portions of the free layer so as to provide an improved exchange coupling.
A method of the invention includes setting the magnetic spins of the sensor portion of the third AFM layer so that an initial setting of the magnetic spins of the first and second AFM layers is not degraded. The first and second AFM layers are set by heat in the presence of a field which is directed parallel to a longitudinal axis of the free layer. This may be accomplished at the wafer level or at the row level where the wafer has been cut into rows of heads. Next, a pulse is conducted through the spin valve sensor via first and second terminals on the wafer and first and second leads to the spin valve sensor causing the free layer to exert a current pulse field on the pinned layer which, in turn, orients the magnetic spins of the third AFM layer in the same direction. The current pulse heats the head discretely throughout sensor portions of the layers of the spin valve sensor and the third AFM layer without unduly heating the first and second AFM layers. Accordingly, the sensor portion of the third AFM layer is set to a perpendicular position without degrading the setting of the longitudinal orientation of the magnetic spins of the first and second AFM layers. The continuous junction spin valve sensor may be either a bottom spin valve sensor where the free layer is closer to the first gap layer than to the second read gap layer or a top spin valve sensor where the free layer is closer to the second read gap layer than to the first read gap layer. The aforementioned method of the invention applies to either a bottom spin valve sensor or a top spin valve sensor.
An object of the present invention is to provide a continuous junction spin valve sensor wherein first and second antiferromagnetic biasing layers longitudinally bias a free layer for stabilizing its performance.
Another object is to employ an antiferromagnetic scheme for effectively longitudinally biasing a free layer and pin a pinned layer of a continuous junction spin valve sensor.
A further object is to provide a method of making a continuous junction spin valve read head wherein the setting of the magnetic spins of first and second antiferromagnetic layers for longitudinally biasing a free layer is not degraded by magnetically setting the magnetic spins of a third antiferromagnetic layer for pinning a magnetic moment of a pinned layer.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.